Towards an image-guided navigation system for rectal cancer surgery

The standard treatment for rectal cancer is surgical resection of the entire rectum with its surrounding fat. Despite this radical procedure, local recurrence may still occur in up to 10% of patients and is often due to incomplete resection of the tumor area. To better assess tumor borders, image-guided navigation (IGN) can be used. A common form of IGN is where the surgeon uses tracked surgical tools that are visualized on a screen in real-time, relative to a 3D anatomical model created from preoperative imaging. To maintain sufficient navigation accuracy, when operating on the non-rigid rectum, the 3D model should be updated upon tumor motion. It was investigated if including real-time tumor tracking, using electromagnetic (EM) trackers placed close or inside the tumor, can facilitate this. Using an IGN system with wired EM tumor tracking, surgeons assessed proximal rectal tumor borders with a low median error of 3mm. Tumor tracker placement and linking it to the 3D model, however, took 30 minutes of intraoperative time. With implantable wireless trackers these steps can be done preoperatively. It was investigated if a commercially available system for wireless EM tumor tracking in radiotherapy (WL-EMTS) can also be used for IGN surgery. An IGN system was developed using the WL-EMTS for tumor tracking and an optical tracking system for tool tracking. With this IGN system it was possible to reduce incomplete resections of non-palpable breast phantom tumors by a factor of 3, compared to a clinically used wireless localization technique. The IGN system was upgraded using only the WL-EMTS for tumor ánd tool tracking. Accurate navigated resections were possible on virtual lesions in ex vivo liver specimens, where surgeons cut with 0.1±2.3mm accuracy along a planned resection margin. Ideally, the 3D model is projected onto the actual anatomy, such that the navigation screen can be omitted, improving usability. In laparoscopic surgeries this requires laparoscope camera calibration. With oblique-viewing laparoscopes, often used in rectal surgery, camera calibration parameters change when rotating their telescope. Therefore, a camera model was developed modeling these changes, resulting in reprojection accuracies of about 4 pixels (0.4mm) independent on telescope rotation.